Shop Windows to the Universe

Magnetic field lines from a computer simulation of the solar corona show some of the complexity of the Sun's magnetic field. Colors on the Sun's surface show the strength of the magnetic field (yellow is largest).
Click on image for full size

Helmet Streamers and the Magnetic Structure of the Corona

The gas in the solar corona is at very
high temperatures (typically 1-2 million
kelvins
in most regions) so it is almost completely in a plasma
state (made up of charged particles, mostly protons and electrons).
Strong magnetic fields thread through the corona. Where these magnetic lines
of force are closed, the magnetic field is strong enough to trap
the solar plasma and keep it from escaping. Plasma accumulates
in these regions and forms the beautiful structures call helmet
streamers seen during solar eclipses.
Prominences are often situated beneath helmet streamers, and active
regions occur beneath streamers near the equator (sometimes called
active regions streamers). In some regions, the coronal magnetic
field cannot confine the plasma, and the plasma expands outward,
reaching supersonic velocities. Regions on the Sun with these
open magnetic field lines (which stretch far out into the solar system)
correspond to coronal holes and are the source of the solar wind, which
accelerates outward from the Sun and fills interplanetary space.
The electrons in the coronal hole plasma are typically cooler and
less dense than streamers,
and so they show up as dark regions in both X-rays and white light.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

You might also be interested in:

Rising above the Sun's chromosphere , the temperature jumps sharply from a few tens of thousands of kelvins to as much as a few million kelvins in the Sun's outer atmosphere, the solar corona. Understanding...more

The Kelvin scale is a temperature scale that is often used in astronomy and space science. You are probably more familiar with the Celsius (or Centigrade) scale, which is part of the metric system of measures,...more

Plasma is known as the fourth state of matter. The other three states are solid, liquid and gas.Almost everything is made up of atoms (your dog, your science book, this computer...). The atom has a nucleus...more

An eclipse of the Sun occurs when the Earth passes through the moon's shadow. A total eclipse of the Sun takes place when the Moon is directly between the Sun and the Earth. When a total eclipse does...more

Solar eclipses are really great to watch! But in the past, people were very scared of them. They didn't understand what was going on. Some people thought that a monster or animal was eating the Sun! They...more

Most of the energy we receive from the Sun is the visible (white) light emitted from the photosphere. The photosphere is one of the coolest regions of the Sun (6000 K), so only a small fraction (0.1%)...more

The gas in the solar corona is at very high temperatures (typically 1-2 million kelvins in most regions) so it is almost completely in a plasma state (made up of charged particles, mostly protons and electrons)....more